The Annual Pattern of Feeding, Growth, and Sexual Reproduction in Cyanea (Cnidaria: Scyphozoa) in the Niantic River Estuary, Connecticut

Abstract

The seasonal occurrence, population dynamics, feeding, growth, reproduction, and timing of planular deposition was determined for a semelparous annual population of Cyanea medusae in the Niantic River estuary, Connecticut, which was sampled for 14 years. The annual pattern was highly predictable. Their ephyrae appear shortly after ice-out in late February, medusae with gonads occur in late April-early May, and are reproductive (bearing planulae on their oral folds) by late May-early June. At this time (early to mid-June), the medusae deteriorate, disappearing from the plankton in late June-early July. Population size, similarly, exhibits small variation, showing only a 5-fold difference in anbundance. With deterioration, the frequency of feeding medusae declines; otherwise, they are opportunistic predators on seasonally numerous zooplankton, including fish. Growth shows two phases: first, a three month period of rapid exponential growth when medusae mature; and second, a one and one half month period of decline in average size of individuals as the larger medusae die. Medusae exhibit a sequence of "organ" loss prior to death: first, the tentacles, then the oral folds, and last, the gonads. Coincident with the disappearance of these organ-deficient medusae from the water column, their planulae first appear attached to shells in the benthos. The deterioration of medusae, and in particular the loss of planulae-bearing oral folds, may be requisite for the mass release of their planulae.